Do you know of any arachnids who ventured towards carcinisation?
no because the term "carcinization" was created to describe the tendency for marine decapod crustaceans to convergently evolve crab-like body plans, it was never supposed to be applicable to other animals!
I blame pop science for spreading it around as a funny term that got misunderstood and misapplied basically from that point onward. most other animal groups don't get their own term for this phenomena and carcinization does NOT apply because... these animals aren't evolving into crabs. only decapods do that ¯\_(ツ)_/¯
(decapods are the marine crustacean group with ten legs- true crabs, lobsters, hermit crabs, robber crabs, mantis shrimp, prawns, slipper lobsters, and all of their infinite assorted relatives in the deep blue sea)
Not only does carcinization only occur in decapod crustaceans, it specifically occurs in the group Anomura, which are the closest living relatives of true crabs, and I would argue that there aren't any anomurans that are particularly non-crablike to begin with. Most anomurans are typically called crabs in English, such as hermit crabs, king crabs, mole crabs, and porcelain crabs. The only anomurans not typically called crabs in English are a few lineages typically called squat lobsters:
Even then, some species of squat lobster (which are not true lobsters) are also called crabs, such as the yeti crab.
The interesting thing about carcinization is not that widely disparate lineages keep evolving into crabs, it is the remarkable specificity of the "crab" body plan that has evolved repeatedly within the true crab+anomuran group, primarily that the carapace is wider than long, the abdomen is extremely reduced in size and tightly folded under the body, and there is a tendency to walk sideways. Trying to find examples of carcinization in other groups of animals by loosening your definition of "crab" to include animals without this specific combination of features is missing the point. Animals are no more likely to evolve to be vaguely crab-shaped than they are to evolve to be vaguely shaped like any other animal.
